Method of sterilizing



METHOD OF STERILIZING Arno Brasch, New York, N.Y., Wolfgang Huber, San Francisco, Calif., and Adnan Waly, Rego Park, N.Y., assignors to Electronized Chemicals Corporation, Brooklyn, N.Y., a corporation of Delaware 1 Claim. (Cl. 99-221) Matter enclosed in heavy brackets If] appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The present invention relates to the elimination or marked suppression of organoleptic changes in substances, particularly foods, which have been sterilized by penetrating radiation of the ionization producing type.

Of the available ionizing radiations, highintensity electrons are particularly well suited for the sterilization of foods and similar substances, because of their predictable penetration range, ease of generation at high energy levels, high biological efiiciency, penetrability of all typesof packing materials, ready control and ease of protection of personnel.

Foodstufis generally are heterogeneous mixtures of ampholytes, electrolytes, nonelectrolytes and inert substances, with the total solid content varying between 5% and 30%. For most such products, commercial sterility canbeobtained with a dose of high intensity electrons equivalent to 1,500,000 REP. The term REP is an abbrevation of Roentgen equivalent physical, a unit indicating the amount of energy absorbed in the form of ionizing radiation. The dose of 1.5 l0 REP is equivalent to about 1.5 10 erg/g, 15 joule/g., 15 w. sec./g., and/or 1.5 X10" B.t.u./g. The fact that the absorption of such a dose produces sterility with a temperature rise of only 3.7 C. in water characterizes this technique as heatless preservation, and thus makes feasible the sterilization of substances in the raw or near raw state.

While the typical chemical and physical changes characteristic of heat processing are absent in irradiation preserved foodstuifs, other, sometimes undesirable, effects on taste, odor, color and texture nevertheless can occur. For convenience, such observable alteration offood or similar substances will be referred to as organoleptic change.

It is the principal object of the present invention to provide a novel process for the sterilization of certain foods or similar substances by ionizing penetrating radiation in which the organoleptic changes frequently accompanying such sterilization are suppressed.

An additional object is to provide a novel process of this character which is particularly adaptable to the packing of meats and meat products and which can be used alone or in conjunction with other processes intended for the same general purpose.

Other objects and advantages will become apparent from the following description of a preferred embodiment of this invention. 7

We have learned that most of the organoleptic changes referred to above which affect the taste, odor and appearance of a substance sterilized by electron bombardment are due to the formation of very small quantities of complex radiation activated oxygen and nitrogen compounds and combinations thereof in or upon the surface of the food substance. As an example, if cuts of meat or ground meat are bombarded with high velocity electrons of sufficient intensity to bring about the sterility of the food product, it is usually found that the surface and to a lesser extent the interior of the meat or meat product becomes somewhat browned and in that the taste and odor, primarily the latter, of the meat substance is somewhat effected in a rather characteristic fashion. It has been found that these changes occur whether or not the meat substance is in the open or is seared within an airtight package, such as a sheet metal packing can, for instance.

The present method, which is particularly adaptable for the packing of meat and meat products largely avoids these organoleptic changes and is carried out in the following fashion. The meat cut or meat product is sealed as quickly as is practicable within a can or other airtight container which is to serve the purpose of preventing recontamination of the food product after it has been sterilized by electron bombardment. In this packing process the container should be reasonably filled, that is, there should be as little air space left within the can as is practically possible so that the quantity of oxygen in association with the meat or meat product is kept to a minimum. After the meat product has been packed in this manner it is set aside under refrigerationif desired it may be frozen-for a period that will vary between about a day on the one hand and as much as four days or so on the other hand, this storage time depending upon the type of meat, its freshness, the amount of air or oxygen present within the can around or dissolved or occluded within the food substance, and the temperature at which it is stored.

After the packaged meat or meat product has been stored for an, interval as indicated above, it then can be subjected to penetrating ionizing radiation in any suitable fashion at sufiicient intensity to bring about sterility of the product without the development of objectionable organoleptic changes.

As specific examples of this method of processing the following are given. If ordinary beef sirloin steak is sealed reasonably soon within an airtight container and then bombarded with sterilizing doses of high velocity electrons to a dose of approximately 1.5)(10 REP, the meat will be considerably browned and will have a characteristic objectionable odor and taste. If such meat identically packed is stored for twenty-four hours at from 3 to -15 C. and then irradiated, the odor and taste are greatly improved although the color still may be considered to be unsatisfactory in that it is browner than raw meat. If such containers of raw beef are stored for seventy-two hours at temperatures between 3 and 180 C. the results are still further improved, with the greatest improvement being noted in the range between -l5 and --180 C. Within this range there is little detectable difference between the treated and untreated raw product. Similar storage for a period of ninety-six hours brings about slight additional improvement, but probably is hardly worthwhile, since the product as pointed out above will be in an excellent condition after storage for seventytwo hours.

Veal, lamb, pork and poultry similarly treated react substantially identically. That is, improvement is noted for a storage period up to about seventy-two hours after which the meat product after irradiation appears, tastes and smells much as the original raw meat and therefore is not susceptible of much additional improvement. Although it is possible by varying the storage conditions for different airtightly packed meats and meat products, depending upon the particular conditions encountered, to give some improvement over a standardized procedure, it will be seen from the above that a thoroughly satisfactory sterile product can be obtained by packing the meat or meat products in an airtight container and storing it for seventy-two hours at -15 C., after which it. is, bombarded with high velocity, electrons. tov a, .dOSQz of 1,500,000- REP.

We believe that the reason ,for:,.this improvement: in .v the, quality: of the packaged and sterilized ,productjs probably dueto, the following phenomenonii The meat, product at the timesit is packed has to some extentiat, least. retained theproperty of. live tissue in. the sensewthat individual cells or, cell components within themeatflor, meat. product are, capable of, metabolic, enzymatic processes. Inv other: words, individual cells, seem-tohave,

someof the properties of life. Because ofsthis iafter the meataor meat product has: been, scaled within -the container and placed in storage for an,interval ,an, appre,

ciable. portoin of these cells, continuetheir metabolic-1 process,,thereby usingup the oxygen. in the containerbv utilizing this oxygenv in thismetabolicrprocess solgthat its,

cannotbe activatedfurther by the radiationrwhichfollowss, It appears, therefore, thatv atthe time-pf irradiation the, meat or meat product is ,for,.all practicaltpurposesnsealed; within an airtightcontainer in which. thereis no: oxygen,

present either in thewgaseousor dissolved state;

Although-we have ascribed the effect described above; largely to the, continuing. metabolic, process, vit; ap;

preciated that the consumption ofv oxygen: in thewsealed v container may in part bendue toanon-enzymatic,chemical action and invfact, it is possiblethat thetnon-enzymaticz action.v maybe largclyresponsiblefor thenresultsv The, importantfact,,however, is, that not only isthe. oxygenin, the .can consumed by the meatorwmeat produCtduriug-the interval of. pro-storage, but that thefhcompoundsn-formed, bysuch oxygen, consumption are. of arstable naturerandr do not break down with subsequent electron bombardement; orsif they do,in..part bre ak-.odown,, thegresulting products, are not v objectionable and are vnot detected Although the process described hast-itssprincipalappliv ma es cation in the packing of 4? 7 meat and meat products and related substances such as fish, shelled eggs, dairy products and the like, we have foundithat the same effect occurs when some vegetables and. fruits are blanched and then stored for a period betweenz-hermetic packing and sterilizing by radiation.

In carryingout theaboveprocessit is important that thc-foodsubstance bepacked under such, conditions vthat the ability-of the. substance to consume oxygen, is not exceededby thee-quantity of oxygen-present.- Under some conditions; therefore, it "is of, advantage to vacuum-pack theiproduct or to packit insome inert gaseous, or liquid. medium; such that the, quantity of oxygen, presentis only that; dissolved/oroccluded inithe food and absorbed to the surface of the food product and its container.

Having described our invention, what we claim as new and useful and desire to secure by Letters Patent of the. United States is:

The method-of, preserving food substances; which 1 comprises hermet-ically r sealing ,the' food substance in a r COn -v tai'nen-storing the-container with the food substance sealed" therein under refrigeration for a period of from [seveuty U two], ;twenty-faunto ninety-six hours to permitthe food substance ftOrCQIU/EN; the contained" atmospheric oxygen, and oxygenabsorbed ,within'the food substance into stable, compounds] whichwdo .not; produce objectionable radiation activatedaoxygen and nitrogen products when subjected to isterilizingdoses :ofi ionizing penetrating-radiation, and finally: subjecting thesealed andaged food substanceto: a :sterilizing ,"dose- 1 ofrionizing; penetrating radiation of the order-of1,5.00,000 RERthrough the wall1of said container.

Brasch, Y .,Fcb., 7, 19,50.- Brasch; v v.., Decn21,, 1948\ 

